1. Field of the Invention
The present invention relates to a control apparatus installed in a hybrid vehicle or in an electric vehicle.
2. Background Art
A control device for electric vehicles, driven by the output of a motor, controls the driving current of motor, which rotates according to the depression of the accelerator pedal. That is, a directing current (control signal) for controlling an inverter, which outputs the driving current of the motor, is output to the inverter for driving the vehicle.
However, during normal operation (that is, the motor is rotating and the vehicle is moving), current supply phases of the power elements in the inverter circuit are shifted to other phases in sequence. However, when climbing a hill, the rotation of the motor will stop if the torque of the motor required for climbing equals or exceeds the maximum torque of the motor. When the motor is stopped, a current passes through a particular power element, that is, the power element supplies current continuously, which results in an abnormal temperature rise in that particular element. Conventionally, power elements with an increased current capacity or cooling devices with an increased cooling capacity are provided in the vehicle in order to overcome the problem of burning out the power elements when current flows through the power element continuously. Such a countermeasure results in an increase in the size, weight, and finally the cost of the devices.
It is therefore an object of the present invention to provide a control apparatus for an electric vehicle which is capable of preventing an increase of the weight of the vehicle and the overheating of the inverter circuit.
In order to attain the above objective, the first aspect of the invention provides a control apparatus for an electric vehicle which has a motor (in the present embodiment, the motor 50) driven by electric power supplied from an inverter (in the present embodiment, the IGBT 40) and which is propelled by an output of said motor, comprising: a power reducing device (in the present embodiment, the control unit 30) for reducing the electric power to be supplied to an electric power element (in the present embodiment, IGBT element) when the temperature of the electric power element of said inverter circuit exceeds a predetermined temperature; a rotation detecting device (in the present embodiment, the rotation sensor 60) for detecting the rotational position of the motor when rotating in the reverse direction after said power reducing element has reduced the electric power supplied to the electric power element; a switching device (such as a control unit 30 in the present embodiment) for switching from the electric power element which currently supplies electric power to the inverter circuit, to another electric power element for supplying electric power in response to the detection of rotation by said rotation detecting device; and an electric power increasing device for increasing or starting the supply of said electric power to said electric power element after said switching device performed the switching.
With the above arrangement, the control apparatus of the electric vehicle of the present invention is provided such that, when the vehicle stops on a steep uphill because the load applied to the motor equals the maximum output of the motor, or when the temperature of an electric element of the inverter circuit exceeds a predetermined temperature, the control apparatus of the electric vehicle reduces or terminates the supply of the electric power to the motor. Accordingly, due to the reduction in the output of the motor, the vehicle starts moving in reverse. Then, the rotational position of the motor in the reverse direction is detected, and, in response to the detected rotation, the electric power element normally supplying power to the inverter circuit is then switched to another element in order to continuously supply power to the motor and maintain the driving force of the vehicle so as to not move backward. The control apparatus of the electric vehicle of the present invention is constituted such that it maintains or increases the current supply to the motor, and since the electric power element, after a switch is made so that it is not the current supply element normally supplying the current is no longer heated, it is possible to protect the elements constituting the inverter circuit from overheating. Thereby, it becomes possible to use an element (for example, an IGBT element), which has a standard low current-carrying capacity for constituting the inverter circuit, which results in a reduction in the cost of the apparatus.
According to the second aspect, in the control apparatus of an electric vehicle according to the first aspect, the electric power reducing device reduces the electric power supplied to said electric element, in any one of the following cases: when the temperature detected by said temperature sensor (such as the temperature sensor 22 in the present embodiment) for detecting the temperature of said electric power element exceeds a predetermined temperature, or when the length of time for supplying electric power by the same power element exceeds a predetermined time (such as the count value of the control unit 30 in the present embodiment).
With the above arrangement, since the control device is constituted such that heat generation of the power elements can be estimated through the detection by the temperature sensor or by the length of time of the supply of the power in the same power supply phase, the temperature of the power element can be controlled according to the generated heat, and the power element can be protected from overheating.